Devices and methods to measure gastric residual volume

ABSTRACT

Devices and methods to measure gastric residual volume (GRV) are described where at least one additive component (a GRV indicator) may be dispersed in a body lumen such as a stomach. The GRV indicator may changes a physical (chemical, electrical, thermal, mechanical, optical, etc.) characteristic within the stomach by a measureable degree. This degree of change and/or the rate of return to the previous state, may be used to determine the GRV of a patient. The determined GRV can also be used to automatically or semi-automatically control the patient&#39;s feeding rate and/or volume and/or frequency to adequately nourish the patient but avoid complications. The physical characteristic(s) may also be used to detect that the feeding catheter or tube is in the correct location (ie stomach vs lung or esophagus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/222,670 filed Jul. 28, 2016, which is a continuation of InternationalApplication No. PCT/US2015/14839 filed Feb. 6, 2015, which claims thebenefit of priority to U.S. Provisional Application No. 61/936,804 filedFeb. 6, 2014, each of which is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to the measuring of gastric volume.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if each suchindividual publication or patent application were specifically andindividually indicated to be so incorporated by reference.

BACKGROUND OF THE INVENTION

Enteral feeding through a feeding tube allows patients to receivenutrition when he/she cannot receive nutrition through the mouth, cannotswallow safely or to provide supplemental nutrition. Current standard ofcare require periodic monitoring of the gastric residual volume (GRV)after feeding. GRV is the volume of residual gastric contents thatremain in the stomach after a certain period of time has elapsed afterfeeding via a feeding tube. The concern is that high GRV values mayindicate pulmonary aspiration, a critical issue that could lead topneumonia with serious consequences. Usually these GRV measurementsoccur every 4-6 hours, and particularly during the first few days ofenteral feeding to allow acceptance of the feeding tube.

The current standard method of determining GRV is via aspiration from anasogastric tube. There are several issues with the current methods ofdetermining GRV including:

1) Aspiration of contents to measure GRV is a burden on nursing staff.Even with expertise in the procedure, the process takes 5 minutes. Withthis repeated every 4-6 hours for every patient requiring GRVmonitoring.

2) The process of aspirating gastric contents through manual mechanicalmeans may increase the incidence of pulmonary aspiration.

3) Lack of standardization of means to manually measure GRV, whetherthrough aspiration by syringe, low-wall suction, gravity drainage orother method, introduce errors in measurement.

A solution is needed which addresses these and other issues withmeasuring GRV in patients.

SUMMARY OF THE INVENTION

The present invention is a GRV measuring device and methods whichdetermine the volume of gastric content by introduction of at least oneadditive component (a GRV indicator) that is dispersed and then changesa physical (chemical, electrical, thermal, mechanical, optical, etc.)characteristic within the stomach contents by a measureable degree. Thedegree of change of this physical characteristic, and/or the rate ofreturn to the previous state, may be used to determine the GRV of apatient. If the GRV is small, the magnitude of change will likely begreater, and the rate of change of this physical characteristic back tobaseline will be slower. If the GRV is large, the magnitude of changewill likely be smaller, and the rate of return to baseline will befaster. The determined GRV can also be used to automatically orsemi-automatically control the patient's feeding rate and/or volumeand/or frequency to adequately nourish the patient but avoidcomplications. The physical characteristic(s) may also be used to detectthat the feeding catheter or tube is in the correct location (ie stomachvs lung or esophagus).

One variation of an apparatus for determining a gastric residual volumemay generally comprise an elongate body which may define at least onelumen therethrough, a medium having one or more GRV indicators which maybe in fluid communication with the at least one lumen, one or moresensors positioned along the elongate body such as at or near a distaltip of the elongate tube, wherein the one or more sensors are configuredto measure a change in a parameter of the GRV indicators, and acontroller in communication with the one or more sensors, wherein thecontroller is configured to determine a GRV based on the change in theparameter of the GRV indicators.

In use generally, such an apparatus may be used to determine the GRV bypositioning the elongate body which may define at least one lumentherethrough into the body lumen, introducing the medium having one ormore GRV indicators such as through the at least one lumen and into thebody lumen, and sensing the one or more GRV indicators via one or moresensors positioned along the elongate body such as at or near a distaltip of the elongate body. The one or more GRV indicators may bemonitored for a change in a parameter of the GRV indicators and the GRVof the stomach may be determined based on the change in the parameter ofthe GRV indicators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the GRV measuring device in a humanstomach.

FIG. 2 shows a stomach into which a substance containing a concentrationof a GRV indicator is introduced.

FIG. 3 shows an embodiment of the GRV measuring device where sensors areoutside of the stomach.

FIG. 4 shows an embodiment of the GRV measuring device where sensors arelocated along the length of the catheter or tube.

FIGS. 5 and 6 show embodiments of the GRV measuring device wheresensor(s) are at different location.

FIG. 7 shows an embodiment of the GRV measuring device which is separatefrom a feeding tube.

FIG. 8 shows a GRV measuring device where the GRV measuring device isinserted through a feeding tube.

FIGS. 9 and 10 illustrate how the sensor(s) of the GRV measuring devicemay be located at various places relative to the feeding tube.

FIG. 10 shows sensor(s) of the GRV measuring device in the pylorus

FIGS. 11-13 show embodiments of the invention in which there is at leastone transmitter and/or receiver to track location of the device withinthe stomach and/or stomach contents.

FIG. 14 shows a graph of the temperature of the stomach contents overtime as sensed by sensor(s) after a bolus of cold substance isintroduced into the stomach.

FIG. 15 shows a graph of the concentration or pH of a GRV indicator overtime after introduction into the stomach.

FIG. 16 shows a graph of the temperature of the stomach contents overtime as sensed by sensor(s) after multiple boluses of cold substance areintroduced into the stomach.

FIGS. 17 and 18 show embodiments of the GRV measuring device for usepercutaneously.

FIG. 19 shows an embodiment of the GRV measuring device for use with ajejunostomy tube.

FIGS. 20-24 show embodiments of the GRV measuring device.

FIG. 25 shows an embodiment of the device where GRV and entry in thestomach is based on a continuously or intermittently monitored physicalcharacteristic.

FIG. 26 shows an embodiment of the device

FIG. 27 is a block diagram of a data processing system, which may beused with any embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an embodiment of the GRV measuring device in a humanstomach. GRV measuring device 108 in this embodiment is a catheter, ortube containing at least one lumen. The GRV measuring device alsoincludes sensor or sensors 110, in this embodiment, at or near thedistal tip of the GRV measuring device. The lumen may be used forfeeding the patient, and/or introducing a GRV indicator into stomach102. Stomach contents 104 include gastric secretions, nutrients whichwere previously present in the stomach, nutrients that have been addedto the stomach via the GRV measuring device or otherwise, as well as anyGRV indicators used to determine the GRV of the stomach.

GRV indicators may include a substance at a higher or lower temperaturethan the stomach contents, a substance at a higher or lower pH than thestomach contents, a substance at a higher or lower O2 concentration thanthe stomach contents, a substance at a higher or lower CO2 concentrationthan the stomach contents, a substance at a higher or lower ion (such asMagnesium) concentration than the stomach contents, a substance at ahigher or lower glucose concentration than the stomach contents, asubstance at a higher or lower viscosity than the stomach contents, etc.Additional GRV and/or stomach entry indicators include electricalproperties (conductance, resistance, current generation based on theacid level, impedance, etc.) that will increase or decrease depending onthe ratio of stomach acid to tube feed in the stomach. Other GRVindicators are also possible and some are described in other embodimentsherein.

GRV indicators may be introduced through the lumen of GRV measuringdevice 108 into stomach contents 104. Sensor or sensors 110 then canmeasure the change in properties of the stomach contents to determinethe Gastric Residual Volume, or GRV, of the stomach.

For example, if a substance is introduced into the stomach which is at ahigher or lower temperature than the stomach contents, the sensor(s) canmeasure the magnitude of change, and/or the rate of change oftemperature of the stomach contents to determine the GRV. Both the rateof initial change, and the rate of change back to the pre-introductionstate can be measured, as well as the magnitude of change. In general,the change from the maximum change, back to the pre-introduction level,is a slower change and easier to measure, but either change can bemeasured. After the GRV indicator is introduced, and the maximum levelof the GRV indicator has been measured, the rate of change of theindicator, or slope of the temperature vs. time curve, can be measured.A relatively steep slope indicates a higher GRV, where a relativelyshallow slope indicates a lower GRV. The same can be done withconcentration and other GRV indicator types. For example, if the GRVindicator is glucose, the sensor(s) would measure the concentration ofglucose within the stomach contents and the change in concentration overtime.

Alternatively, a bolus of a substance at a fixed temperature (orconcentration, etc., depending on the GRV indicator) can be introducedinto the stomach and the temperature (or concentration, etc.) of thestomach contents can be measured as soon as the contents have had achance to mix. The relatively immediate magnitude of change intemperature or concentration may also be an indicator of the GRV of thestomach. The lower the GRV, the greater the impact the introduction ofthe GRV indicator will have on the stomach contents. The higher the GRV,the lower the impact will be, resulting in a lower magnitude of measuredchange of the GRV indicator.

Another embodiment of the GRV measuring device includes a temperaturechanging mechanism as part of the device. In this embodiment, thetemperature of the stomach contents may be altered by either a heatingor cooling element. For example, GRV measuring device 108 may include aheating element (not shown) which heats the contents of the stomach. Thechange of temperature is measured over time and the rate and/ormagnitude of the temperature change as the stomach contents heat and/orcool can be used to determine the GRV of the stomach.

Another variation of this embodiment of the GRV measuring devicemeasured pH instead of temperature. A substance of a certain pH (higheror lower than that of the stomach contents) can be introduced into thestomach, and the change in pH measured over time to determine the GRV ofthe stomach.

A controller (not shown) may be used as part of the GRV measuring deviceto record and/or interpret the various levels of GRV indicator(s)measured by sensors within the stomach. The controller may also use theGRV info to control feeding volume/rate/frequency/contents.

FIG. 2 shows a stomach into which a substance containing a concentrationof a GRV indicator is introduced and the concentration measured overtime within the stomach contents. In this embodiment, the sensor(s)measure concentration instead of temperature. For example, GRV indicator202 in this embodiment may be glucose, or magnesium, or any othersuitable substance, the concentration of which can be measured.

FIG. 14 shows a graph of the temperature of the stomach contents overtime as sensed by the sensor(s) and recorded and/or interpreted by thecontroller after a bolus of cold liquid is introduced into the stomach.The magnitude of the temperature drop and the slope of the gradualtemperature rise back to normal can be used either together, orseparately, to determine the GRV of the stomach.

FIG. 15 shows a similar graph for the introduction of a GRV indicatorfor which the concentration or pH is measured. After introduction of theGRV indicator into the stomach, the concentration or pH rises, and thengradually returns to normal over time. Again, the magnitude of thechange and the slope of the return to normal of the concentration or pHof the GRV indicator within the stomach can be used together, orseparately, to determine the GRV of the stomach.

FIG. 16 shows a graph of the temperature of the stomach contents overtime as sensed by the sensor(s) and recorded and/or interpreted by thecontroller after multiple boluses of cold liquid are introduced into thestomach. Note that in this example, the magnitude and/or slope of thegraph after each bolus may be utilized by the controller, in addition tothe overall magnitude and slope of the boluses combined. Multipleboluses may be used with other GRV indicators as well.

FIG. 3 shows an embodiment of the GRV measuring device where sensors 302are outside of the stomach, and preferably outside the patient's body.This embodiment is limited to GRV indicators which can travel throughtissue such as temperature, radiation, sound waves, magnetic substances,etc.

FIG. 4 shows an embodiment of the GRV measuring device where the sensorsare located along the length of the catheter or tube. In thisembodiment, the GRV indicator can be measured at different locationswithin the stomach, providing more information regarding the GRV. Forexample, assuming the patient is upright and the stomach contents are atthe bottom of the stomach, the GRV indicator readings at the moreproximal end of the GRV measuring device would be much lower, or evennull, where the measurements at the distal end of the device wouldchange over time as the GRV indicator is introduced and diluted by thestomach contents. Depending on the different GRV indicator measurementsat different locations along the GRV measuring device, more informationcan be obtained about the volume of the contents in the stomach. Forexample the device may be able to determine that the stomach isapproximately half full etc.

FIGS. 5 and 6 show embodiments of the GRV measuring device where thesensor(s) are at different location. FIG. 5 shows sensor(s) 502 on theoutside of tube/catheter. Note that in any of the embodiments herein thesensor(s) may run radially around the tube/catheter or be on one or moresides of the catheter/tube. This, and other embodiments, also allows fora separate feeding tube to be inserted through the GRV measuring device(not shown). This may be desirable where a standard feeding tube isbeing used. Also, it is possible to insert the GRV measuring device intothe patient over a feeding tube that is already in place. This would beadvantageous when it is not known at the time of placement of thefeeding tube that the GRV measuring device will be used.

FIG. 6 shows sensor(s) 602 embedded in the wall of the GRV measuringdevice. This embodiment offers the advantage of a smooth transition onboth the outside and the inside of the GRV measuring device. Note thatthe sensor(s) in any of the embodiments may be at any location along thelength of the GRV measuring device.

FIG. 7 shows an embodiment of the GRV measuring device which is separatefrom the feeding tube. In this embodiment, feeding tube 706 may beinserted into the patient separately from GRV measuring device 702. GRVmeasuring device in this embodiment may or may not have a lumen. Sincethe feeding of the patient occurs through a separate tube, the size ofthe GRV measuring device can be much smaller and be inserted alongsideof the feeding tube. In fact, GRV measuring device in this embodimentmay be similar dimensions to a guide wire (down to 0.5 mm or less, or1.0 mm or less, or 2.0 mm or less) with sensor(s) 704 at its distal endor along its length. In this embodiment the GRV indicator may beintroduced through the separate feeding tube.

FIG. 8 shows a GRV measuring device similar to that of FIG. 7, howeverin this figure, the GRV measuring device is inserted through the feedingtube. This configuration has the advantage of easily being insertedafter the feeding tube is already in place. In this and any of theembodiments the GRV measuring device may be introduced only periodicallybefore or after the GRV indicator is introduced into the stomach. Inthis way, the extra bulk of the GRV measuring device does notsignificantly interfere with the feeding process through the feedingtube. Alternatively, the GRV measuring device may be small enough to notadversely impact the flow of nutrients or other substances through thefeeding tube. The GRV measuring device in this and other embodiments mayhave a curved tip, or a J-tip to help maneuver it through and out theopening of a feeding tube.

Note also that the GRV measuring device shown here may also be used toconfirm location of the device in the stomach, vs. the lungs oresophagus (discussed in more detail herein). In this scenario, the GRVmeasuring device may be placed first, with confirmation of placement inthe stomach by using sensor(s). The feeding tube may then be placed overthe GRV measuring device so that the placement of the feeding tube inthe stomach is also confirmed. In this embodiment, the GRV measuringdevice would need to be long enough (or extendable) to allow the user tothread the feeding tube over the GRV measuring device and into thestomach. For example, in an embodiment where the feeding tube isthreaded over the GRV measuring device, the GRV measuring device (orextended GRV measuring device) would preferably be at least about twicethe length of the feeding tube. For a child, the length may be at leastabout 75 cm, for an adult the length may be at least about 180 cm, or atleast about 200 cm or at least about 280 cm. A GRV measuring deviceextension may be a wire that is either permanently, or removably,attachable to the end of the GRV measuring device to extend it.

In embodiments of the GRV measuring device where it is placed after thefeeding tube, the length can be shorter, for example, for a child, atleast about 40 cm, or for an adult, at least about 95 cm, or at leastabout 110 cm, or at least about 140 cm.

FIGS. 9 and 10 illustrate how the sensor(s) of the GRV measuring devicemay be placed at various places relative to the feeding tube. This mayhelp obtain cleaner measurements after introduction of the GRVindicator. For example, if a heated substance is introduced through thefeeding tube, it may be advantageous to have the sensors of the GRVmeasuring device some distance away from the exit of the feeding tube,both to protect the sensors from extreme heat, but also to get a cleanertemperature reading. More mixing of stomach contents will have occurredthe further from the source of the GRV indicator introduction thesensor(s) are.

Alternatively the sensors may be placed within the feeding tube when theGRV indicator is introduced through the feeding tube to obtain abaseline reading of the temperature/concentration/pH etc. of the GRVindicator. The sensors may then be moved into the stomach contents toobtain the changing readings which will be used to determine GRV.Alternatively, the GRV measuring device may have sensors along itslength to achieve the same thing. There may be other advantages tomoving the GRV measuring device during the measurement process.Measuring the GRV indicator at different places within the stomachand/or stomach contents will provide more information about the stomachcontents.

FIG. 10 shows sensor(s) 1102 of the GRV measuring device in the pylorus1004. In this embodiment, the stomach content volume is estimatedthrough direct measurement of the input volume (enteral feedingmaterial) and output volume (pylorus transit). The amount of materialentering and passing through the pylorus may be measured with avolumetric flow meter, or Doppler ultrasound, or optics, or any othersuitable technology. In one embodiment, after magnetic materials areintroduced into the stomach, the movement of the materials induces acurrent as it passes the pylorus transit which can be measured eitherwithin the pylorus, or outside of the patient.

Note that in any of the embodiments herein, the GRV measuring device maybe outside of, inside of, incorporated into or completely separate fromthe feeding tube.

Other embodiments of the invention are shown in FIGS. 11-13. In theseembodiments, the GRV measurement device is also used to locate thedevice, or a feeding tube, within the stomach to ensure proper feedingand GRV measurements. In these embodiments transmitters 1102 give off asignal which is detected by location receivers 1106. The transmittersmay be separate from the sensor(s) shown in other embodiments, howeverboth may be present on the GRV measuring device (note that the sensor(s)are not shown in FIGS. 11-13). The location receivers may exist outsidethe body as shown in FIGS. 11 and 12, or they may be part of the GRVmeasuring device, as shown in FIG. 13. The transmitted signal may be asound signal, an ultrasound signal, a pressure signal, or any othersuitable signal. Alternatively, or in addition, pH, temperature, or anyof the GRV indicator signals may be used. The location receivers receivethe signal either through the tissue, as shown in FIGS. 11 and 12, orafter reflected signal 1302 has bounced off of the walls of the stomachand possibly the stomach contents, as shown in FIG. 13. The embodimentof the GRV measuring device in FIG. 13 includes both the transmittersand the location receivers on the device within the stomach.

FIGS. 11 and 12 show the transmitter in the empty part of the stomachand the stomach contents, respectively. The signal received when thetransmitter is in these two different locations will be very different,and will aid in locating the tip of the feeding tube. The transmittersmay be at the tip of the feeding tube, and/or may be elsewhere relativeto the tip of the feeding tube.

FIGS. 17 and 18 show embodiments of the GRV measuring device being usedpercutaneously. For example, the GRV measuring device can be used as, orin conjunction with, a Percutaneous Endoscopic Gastrostomy, or PEG,tube. In this situation the feeding tube goes through the abdomen of thepatient, directly into the stomach, to feed the patient. Shown here isPEG tube 1702 going through skin 1708, fat 1706 and muscle 1704 andthrough the stomach wall so that the tip of the PEG tube is in thestomach. The GRV measuring device may be incorporated into the PEG tube,or may be separate as shown here. GRV measuring device 1712 is shownhere being used through the inside of a PEG tube. In this and otherembodiments the GRV measuring device is connected to a controller torecord and/or interpret the measurements sensed by the sensors.

In this and other embodiments, GRV measuring device may be in thestomach throughout feeding, or it may be introduced periodically whenmeasurements are desired. Restrictor 1710 may be used to control theflow of nutrients into the stomach. The restrictor may be controlled bythe controller in a feedback loop so that nutrients are only introducedwhen the GRV is at or below a certain level. Nutrients may also beautomatically limited when the GRV is at or above a certain level. Theselevels may be preset, or may be set by the controller and can beadjusted as necessary. This type of feedback control also allows forbolus feeding vs. continuous feeding which is more physiologicallyrepresentative.

FIG. 18 is similar to FIG. 17 except that the entrance point for the GRVmeasuring device is between the patient and the resistor. This allowsthe resistor to be more easily used when the GRV measuring device is inplace.

Note that the embodiments in FIGS. 17 and 18 can be used with a standardPEG tube. Alternatively, the GRV measuring device may be incorporatedinto a PEG tube.

FIG. 19 shows an embodiment of the GRV measuring device for use with ajejunostomy tube. In this embodiment the feeding tube enters theintestines rather than the stomach. Similar to other embodiments herein,the GRV measuring device may be used with a standard jejunostomy tube,or may be incorporated into a jejunostomy tube.

FIGS. 20-24 show detailed embodiments of the GRV measuring device. FIG.20 shows an embodiment of the GRV measuring device which is incorporatedinto a feeding tube. Device shaft 2002 includes sensor or sensors 2204,measurement communication line 2006, which may be a metal wire, as wellas feeding lumen 2008. Sensor(s) 2004 measure the temperature, pH,concentration etc. of the GRV indicator in the stomach after theindicator is introduced through the device or created by the device. Forexample, a fluid below body temperature may be introduced into thestomach through lumen 2008. The magnitude of the change of temperaturewithin the stomach is measured by sensor(s) 2004, as well as the rate ofreturn to normal temperature. This information is transferred alongcommunication line 2006, along shaft 2002 back to the controller. Thecontroller may control the feed supply either with user input, orautomatically, depending on the gastric volume analysis of thecontroller.

Note that sensor(s) 2004 may be placed anywhere along the length of thedevice. Also note that sensor(s) may be placed on either the inside ofthe device (within lumen 2008) or on the outside, or both. Havingseparate sensors on both the inside and outside of the device may allowmeasurements of the untainted GRV indicator as it is entering thestomach (inside sensors) as well as measurements of the change in theGRV indicator over time (outside sensors). These sensors may be the samesensor, where it measures both inside the device, and outside thedevice. Also note that there may be a barrier or insulator between thesensor and either the inside of the device, or the outside of thedevice. This would allow the sensor to measure the GRV indicator oneither the inside of the device or the outside of the device withoutbeing tainted.

Alternatively the GRV measuring device may cause a cooling of thestomach contents with a cooling element (not shown) on the device, andmeasure the resulting magnitude and rate of temperature change todetermine gastric volume.

In another example, the pH of the stomach contents may be measured todetermine gastric volume. A substance of a known pH (which may be thefeeding substance itself) is introduced into the stomach, and thesensor(s) measure the change in pH and the rate of return to normal pH,send the information back to the controller, and the controller can thendetermine gastric volume.

In another embodiment, the GRV measuring device may use more than oneGRV indicator. For example, both temperature and pH may be used. In thisexample, measurement of one GRV indicator may be used to confirm themeasurement of the other GRV indicator for a more accurate result. Inaddition, the measurements may be taken at different locations to assurestomach content mixing and/or to improve accuracy. Other GRV indicatorsmay be combined in a similar manner.

FIG. 21 shows another embodiment of the GRV measuring device. Thisembodiment is designed to be used with a feeding tube, either alongsideit or through the lumen of a feeding tube. This embodiment may be of arelatively small diameter (down to 0.5 mm or less, or 1.0 mm or less, or2.0 mm or less) so that it does not substantially impede the flow ofnutrients to the patient through the feeding tube, or is not difficultto insert into the patient alongside a feeding tube. Shaft 2102 ispreferably relatively stiff, similar to a guidewire, and incorporatesthe signal communication from sensor(s) 2104. Shaft 2102 may be made outof metal such as stainless steel or other appropriate material. In thisembodiment, the GRV indicator may be introduced through the separatefeeding tube. Note that this and other embodiments may be placed intothe stomach before or after the feeding tube is placed in the stomach.

FIGS. 22-24 show another embodiment of the GRV measuring device whichcan be used in conjunction with a feeding tube after the feeding tube isalready inserted. This embodiment is designed to go on the outside of afeeding tube and includes relatively stiff shaft 2208, sheath 2204,sensor(s) 2202 and slit 2206. Shaft 2208 may be made out of similarmaterials to shaft 2102 in FIG. 21. Sheath 2204 is preferably thinenough so that it can easily be slid over a feeding tube, yet rigidenough so that it does not collapse. Various polymers and othermaterials may be used. To introduce this embodiment after a feeding tubeis already in place, sheath 2204 is placed over the outside of theproximal end of the feeding tube using slit 2206. The GRV measuringdevice is then slid down the outside of the feeding tube into thestomach of the patient using the relatively rigid shaft 2208.

FIG. 23 shows this embodiment of the GRV measuring device after it isplaced over feeding tube 2302.

FIG. 24 is a cross sectional view of this embodiment of the GRVmeasuring device.

FIG. 25 shows an embodiment of the device where GRV and entry in thestomach is based on a continuously or intermittently monitored physicalcharacteristic. In this embodiment, the GRV indicator may be inherent inthe feed or meal itself. In this embodiment, the GRV indicator may be aphysical characteristic such as temperature, pH, or electricalresistance, impedance or conductance, etc. In this embodiment, thephysical characteristic may be monitored over time and the changes thatoccur as the meal empties from the stomach may be recorded. As the mealleaves the stomach and the relative concentration of gastric fluidincreases the physical characteristic is altered in a measureable way.In one embodiment, the physical characteristic is pH wherein the pHdecreases as the meal leaves the stomach and the gastric secretionsrepresent more of what is left in the stomach. Once the pH reaches asufficiently low level the device may alert the user that the meal hasleft the stomach and the patient is ready for another bolus. In anotherembodiment the physical characteristic is resistance or impedance. Themeal delivered to the patient may be formulated to have high resistanceor impedance so that subsequent decreases will indicate increasingconcentration of gastric secretions. The opposite is true ofconductance, which may increase as the meal leaves the stomach.

In yet another embodiment, the sensor may consist of a circuit that ispowered by acid. For example, two leads may be introduced into thestomach consisting of different metals (in the preferred embodimentthese are copper and magnesium) In the presence of acid, these metalsact like the terminals of a battery and create a current. This currentcan be continuously or intermittently recorded and report the emptyingof the stomach based on the increased concentration of acid. The sameelectrodes may also be used to sense the electrical parameters(impedance, conductance, resistance. Etc.) of the stomach to providefurther information to help increase the sensitivity and specificity ofthe measurement. Each of these measurements of the physicalcharacteristics of the stomach may be used, alone or in combination, toreport that the sensor (and therefore the tube or catheter tip) is inthe stomach and not in the lung. Ideally two or more parameters aremeasured (pH, current due to acid, impedance/conductance, etc.) toimprove the accuracy of the measurement. This is important as theincidence of tube placement in the lung is as high as 20% and startingtube feeds with the tip in the lung can be fatal. In this embodiment,the sensors may be incorporated into the catheter/tube itself or may bea separate component that is threaded down the inside of an existingfeeding catheter/tube to provide a spot reading as to the location ofthe tip of the tube. In the ideal embodiment, the sensor(s) is/areintegrated into the catheter/tube to first provide an indication thatthe catheter/tube is in the stomach (and not the lung) and then providea signal to indicate the GRV to help optimize feeding. In the idealembodiment, as well, the feeding may be accomplished via a closed loopsystem that will automatically detect the GRV and deliver tube feed whenappropriate based on the programmed nutritional goals for each patient.In this embodiment, target volumes of tube feed may be set per period oftime and maximum volumes may be programmed.

FIG. 25 shows a patient with GRV measuring device 2506 placed in stomach2502. Note the proximity of lungs 2504 and why it is important to beable to confirm placement of the GRV measuring device in the stomach,rather than the lungs or the esophagus. The GRV is measured as discussedherein. Controller 2508 may intermittently or continuously track the GRVvia connector 2510 and using this information, control the feeding ofthe patient via valve or restrictor 2514 using connector 2512. Note thatthe connectors may be wired, as shown here, or wireless. Feed supply2516 is connected to the feeding tube and the volume, rate, frequency,and content of the feed is controlled by controller 2508. GRV indicatorsmay be inherent in the feed, added to the feed, or added independentlyof the feed. The controller may collect measurements of the GRVindicator inside the feeding tube, just before the feed is released intothe stomach, as well as within the stomach contents over time. Thisprovides the controller with a reading of the GRV indicator just beforemixing begins, to provide an accurate GRV.

Note that the sensor(s) on the GRV measuring device may also be used toconfirm placement of the GRV measuring device and/or feeding tube in thestomach, and not in the lungs or esophagus. For example, if the GRVindicator is pH or the presence of certain ions, these measurements willbe different in the stomach, than they are in the lungs or esophagus,even before the GRV indicator is introduced into the feeding lumen. Inthis way, the GRV measuring device can determine placement of thefeeding tube/device in the stomach and determine GRV. The sensors may bethe same type of sensors, i.e. pH or ions, or there may be sensor(s) onthe device for placement, and a separate type of sensor(s) for measuringthe GRV indicator. For example, pH sensor(s) may measure placement ofthe device, and temperature sensor(s) may measure the GRV indicator(temperature) to determine GRV.

FIG. 26 shows an embodiment of the GRV measuring device which uses thegastric acid in the stomach to create a sort of battery which creates ameasurable current which is measured and analyzed by a controller. Themeasured current is indicative of the GRV in the stomach. GRV measuringdevice shaft 2602 contains wires 2608 and 2610 which connect to twodifferent electrodes, 2606 and 2604. The electrodes in this embodimentare made from dissimilar metals, such as Aluminum and Copper, but otherdissimilar metals may be used. The current between the two electrodes issensed by current sense resister 2612. In this embodiment, current isgenerated by the fluid in the stomach, and measured and analyzed by thecontroller to determine GRV.

In an alternative embodiment, the impedance of the stomach fluid ismeasured instead of current. The impedance is indicative of the ratio ofgastric acid to feed, providing an estimate of GRV. This embodimentwould look similar to the embodiment shown in FIG. 26 except that theelectrodes would preferably be of the same metal rather than dissimilarmetals. The controller would generate a voltage and measure theresulting current to determine the impedance of the fluid in thestomach. In this embodiment, voltage is generated by the controller, andcurrent is passed through the fluid in the stomach and the resistance ismeasured and analyzed by the controller to determine GRV.

Using the different electrical properties of the gastric acid in thestomach and the feed, GRV can be estimated by conductivity, current,impedance, capacitance, electrical resistance etc. AC and/or DC signalscan be used to make these measurements. Several possible embodiments areenvisioned. For example:

In one embodiment, an additive liquid element (such as water, saline orsimilar) is introduced by the source that is significantly lower orsignificantly greater in temperature then the nominal contenttemperature. Measurement of the temperature may be recorded by sensorsin one or more locations in the content mixture. In one embodiment, therate of change in temperature over a period of time indicates thegastric volume. In one embodiment, the resulting temperature from themixture after a set period of time indicates the gastric volume. In oneembodiment, a physical thermal element introduces a sudden temperaturechange. This element quickly could heat or chill the gastric contents incontact with the element.

In one embodiment, an additive element is introduced that changes theviscosity of the contents. The resulting change in viscosity indicatesthe gastric volume. In one embodiment, the additive component glucose isintroduced. The resulting change in concentration of glucose indicatesthe gastric volume. In one embodiment, coloring elements such asmethylene blue is introduced and the resulting concentration is used toindicate gastric volume. In one embodiment, an additive component isintroduced that changes the pH value of the gastric contents. The rateof change or resulting pH value indicates gastric volume. In oneembodiment, an additive element is introduced that changes theconductivity of the contents. In one embodiment, an additive element isintroduced that changes the refractive index, opacity, absorptivity,luminosity or color of the contents. In one embodiment, an additiveelement is introduced that changes the specific gravity of the contents.

In one embodiment, an additive component is introduced that causes thecontents to change and is measure through a method of titration. In oneembodiment, the additive component causes contents to solidify. In oneembodiment, the additive component causes contents to changeconductivity. In one embodiment, the additive component causes contentsto change optical opacity or color.

In one embodiment, pressure is introduced by introducing additionalmaterial into the gastric space. This material may be air, saline,water, or other. In one embodiment, pressure may be introduced byinflation of a balloon. In one embodiment, pressure response is measuredinternally. In one embodiment, pressure is measured externally withpressure gauges around the abdomen. This pressure difference before andafter introduction will indicate volume.

In one embodiment, an acoustic source is used to produce standing wavesin the gastric space. The resulting pattern of pressure indicates thedimensions of the media, in this case the gastric contents. In oneembodiment, the acoustic source is external and an acoustic or pressuresensors are used internally. In one embodiment, both the source andsensors are internal. In one embodiment, the source is internal and thepressure or acoustic signature can be measured externally. In oneembodiment, both the source and the sensor are external. The acousticsource may be a point source or an array of transducers that produce arange of frequencies and amplitudes. The acoustic or pressure sensor maybe a single point of measurement or an array of sensors.

In one embodiment, the flow rate of material is measured directly in thepylorus transit. The stomach content volume is estimated through directmeasurement of the input (enteral feeding material) and output (pylorustransit). In one embodiment, the amount of material entering and passingthrough the pylorus is measured with a volumetric flow meter. In oneembodiment, Doppler ultrasound is used to measure fluid movement rate.In one embodiment, after magnetic materials are introduced into thestomach, the movement of the materials induces a current as it passesthe pylorus transit. In one embodiment, optics are used to measure flowrate.

In one embodiment, an autonomous device travels within the gastric spaceto ensure all of the gastric contents are aspirated.

Example of Data Processing System

FIG. 27 is a block diagram of a data processing system, which may beused with any embodiment of the invention. For example, the system 2700may be used as part of a controller which interprets the signals of theGRV measuring device. Note that while FIG. 27 illustrates variouscomponents of a computer system, it is not intended to represent anyparticular architecture or manner of interconnecting the components; assuch details are not germane to the present invention. It will also beappreciated that network computers, handheld computers, mobile devices,tablets, cell phones and other data processing systems which have fewercomponents or perhaps more components may also be used with the presentinvention.

As shown in FIG. 27, the computer system 2700, which is a form of a dataprocessing system, includes a bus or interconnect 2702 which is coupledto one or more microprocessors 2703 and a ROM 2707, a volatile RAM 2705,and a non-volatile memory 2706. The microprocessor 2703 is coupled tocache memory 2704. The bus 2702 interconnects these various componentstogether and also interconnects these components 2703, 2707, 2705, and2706 to a display controller and display device 2708, as well as toinput/output (I/O) devices 2710, which may be mice, keyboards, modems,network interfaces, printers, and other devices which are well-known inthe art.

Typically, the input/output devices 2710 are coupled to the systemthrough input/output controllers 2709. The volatile RAM 2705 istypically implemented as dynamic RAM (DRAM) which requires powercontinuously in order to refresh or maintain the data in the memory. Thenon-volatile memory 2706 is typically a magnetic hard drive, a magneticoptical drive, an optical drive, or a DVD RAM or other type of memorysystem which maintains data even after power is removed from the system.Typically, the non-volatile memory will also be a random access memory,although this is not required.

While FIG. 27 shows that the non-volatile memory is a local devicecoupled directly to the rest of the components in the data processingsystem, the present invention may utilize a non-volatile memory which isremote from the system; such as, a network storage device which iscoupled to the data processing system through a network interface suchas a modem or Ethernet interface. The bus 2702 may include one or morebuses connected to each other through various bridges, controllers,and/or adapters, as is well-known in the art. In one embodiment, the I/Ocontroller 2709 includes a USB (Universal Serial Bus) adapter forcontrolling USB peripherals. Alternatively, I/O controller 2709 mayinclude an IEEE-1394 adapter, also known as FireWire adapter, forcontrolling FireWire devices.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the above discussion, itis appreciated that throughout the description, discussions utilizingterms such as those set forth in the claims below, refer to the actionand processes of a computer system, or similar electronic computingdevice, that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The techniques shown in the figures can be implemented using code anddata stored and executed on one or more electronic devices. Suchelectronic devices store and communicate (internally and/or with otherelectronic devices over a network) code and data using computer-readablemedia, such as non-transitory computer-readable storage media (e.g.,magnetic disks; optical disks; random access memory; read only memory;flash memory devices; phase-change memory) and transitorycomputer-readable transmission media (e.g., electrical, optical,acoustical or other form of propagated signals—such as carrier waves,infrared signals, digital signals).

The processes or methods depicted in the preceding figures may beperformed by processing logic that comprises hardware (e.g. circuitry,dedicated logic, etc.), firmware, software (e.g., embodied on anon-transitory computer readable medium), or a combination of both.Although the processes or methods are described above in terms of somesequential operations, it should be appreciated that some of theoperations described may be performed in a different order. Moreover,some operations may be performed in parallel rather than sequentially.

What is claimed is:
 1. An apparatus for determining a gastric residualvolume (GRV), comprising: an elongate body having a length; one or moreGRV sensors positioned along the elongate body, wherein the one or moreGRV sensors are configured to measure a change in a GRV parameter whenpositioned within a body lumen of a subject; one or more placementsensors positioned along the elongate body, wherein the one or moreplacement sensors are configured to measure a change in a physiologicalparameter when positioned within the body lumen; and a controller incommunication with the one or more GRV sensors and the one or moreplacement sensors, wherein the controller is configured to determine aGRV based on the change in the GRV parameter, and wherein the controlleris further configured to confirm a location of the elongate body withinthe subject during use based upon the change in the physiologicalparameter.
 2. The apparatus of claim 1 further comprising a mediumhaving one or more GRV indicators for introduction into the body lumen.3. The apparatus of claim 1 wherein the one or more placement sensorsare further configured to measure a change in a second physiologicalparameter relating to the physical characteristics.
 4. The apparatus ofclaim 3 wherein the two placement parameters comprise conductivity orimpedance, and temperature
 5. The apparatus of claim 1 wherein thecontroller is configured to determine the change in the GRV parameter orthe physiological parameter during positioning of the elongate bodywithin the subject.
 6. The apparatus of claim 1 wherein the controlleris configured to determine the change in the GRV parameter orphysiological parameter continuously.
 7. The apparatus of claim 1wherein the controller is configured to determine the change in the GRVparameter and physiological parameter continuously.
 8. The apparatus ofclaim 1 wherein the one or more GRV sensors and the one or moreplacement sensors are the same.
 9. The apparatus of claim 8 wherein theone or more GRV sensors and the one or more placement sensors areconfigured to sense impedance or conductivity.
 10. The apparatus ofclaim 1 wherein at least one of the GRV sensors and the one or moreplacement sensors are different from one another.
 11. The apparatus ofclaim 1 wherein the elongate body defines at least one lumentherethrough.
 12. The apparatus of claim 11 wherein a medium having oneor more GRV indicators is in fluid communication through the at leastone lumen.
 13. The apparatus of claim 11 wherein the one or more GRVsensors are positioned within the at least one lumen.
 14. The apparatusof claim 13 wherein the controller is configured to measure an initialbaseline GRV parameter from the one or more GRV sensors.
 15. Theapparatus of claim 1 wherein the one or more GRV sensors are positionedalong an external surface of the elongate body.
 16. The apparatus ofclaim 15 wherein the one or more GRV sensors are embedded along theexternal surface of the elongate body in a smooth transition.
 17. Theapparatus of claim 1 further comprising a restrictor in communicationwith the elongate body, wherein the restrictor is configured to controla flow of a medium through the elongate body.
 18. The apparatus of claim17 wherein the restrictor is configured to be controlled via thecontroller through a feedback loop.
 19. The apparatus of claim 18wherein the feedback loop comprises an upper cutoff limit.
 20. Theapparatus of claim 18 wherein the feedback loop comprises a lower cutofflimit.
 21. The apparatus of claim 18 wherein the flow of medium iscontrolled based upon the GRV.
 22. The apparatus of claim 17 wherein thecontroller is configured to meter the flow of the medium into boluses.23. The apparatus of claim 17 wherein the controller is configured tometer the flow of the medium into a continuous flow.
 24. The apparatusof claim 17 wherein the controller is configured to control a content ofthe medium.
 25. The apparatus of claim 1 further comprising aninflatable balloon positioned along the elongate body and incommunication with the controller.
 26. A method of determining a gastricresidual volume (GRV) in a body lumen, comprising: measuring a change ina physiological parameter within the body lumen via one or moreplacement sensors positioned along an elongate body; confirming alocation of the elongate body within the body lumen based upon thechange in the physiological parameter; sensing a GRV parameter from amedium having one or more GRV indicators within the body lumen via oneor more GRV sensors positioned along the elongate body; monitoring theone or more GRV indicators for a change in the GRV parameter; anddetermining a GRV of the body lumen based on the change in the GRVparameter.
 27. The method of claim 26 further comprising introducing themedium having the one or more GRV indicators through the elongate bodyand into the body lumen prior to sensing the GRV parameter.
 28. Themethod of claim 26 wherein measuring the change in the physiologicalparameter comprises measuring a change in a second physiologicalparameter of the body lumen.
 29. The method of claim 28 whereindetecting two placement parameters comprises detecting conductivity orimpedance, and temperature
 30. The method of claim 26 wherein monitoringthe one or more GRV indicators comprises monitoring for the change inthe GRV parameter or physiological parameter while positioning theelongate body within the body lumen.
 31. The method of claim 26 whereinmonitoring the one or more GRV indicators comprises monitoring for thechange in the GRV parameter or physiological parameter continuously. 32.The method of claim 26 wherein monitoring the one or more GRV indicatorscomprises monitoring for the change in the GRV parameter andphysiological parameter continuously.
 33. The method of claim 26 whereinsensing the GRV parameter further comprises sensing the GRV parameter orthe physiological parameter.
 34. The method of claim 33 wherein sensingthe GRV parameter or the physiological parameter comprises sensing forimpedance or conductivity.
 35. The method of claim 26 wherein the one ormore placement sensors and the GRV sensors are the same.
 36. The methodof claim 26 wherein sensing the GRV parameter comprises sensing via theone or more GRV sensors positioned within the elongate body.
 37. Themethod of claim 36 further comprising measuring an initial baseline GRVparameter from the one or more GRV sensors.
 38. The method of claim 26wherein the one or more GRV sensors are positioned along an externalsurface of the elongate body.
 39. The method of claim 38 wherein the oneor more GRV sensors are embedded along the external surface of theelongate body in a smooth transition.
 40. The method of claim 27 whereinintroducing the medium comprises controlling a flow of the mediumthrough the elongate body via a restrictor in communication with theelongate body.
 41. The method of claim 40 wherein controlling the flowof the medium comprises controlling the restrictor through a feedbackloop via a controller.
 42. The method of claim 41 wherein the feedbackloop comprises an upper cutoff limit.
 43. The method of claim 41 whereinthe feedback loop comprises a lower cutoff limit.
 44. The method ofclaim 41 wherein the flow of medium is controlled based upon the GRV.45. The method of claim 27 wherein introducing the medium comprisesmetering the flow of the medium into boluses.
 46. The method of claim 27wherein introducing the medium comprises metering the flow of the mediuminto a continuous flow.
 47. The method of claim 27 wherein introducingthe medium comprises controlling a content of the medium.
 48. The methodof claim 26 wherein the elongate body further comprises an inflatableballoon positioned along the elongate body.